1. Field of the Invention
The present invention relates to a color display method for specifying a plurality of color tones on a display, such as on an LCD display. Furthermore, the present invention relates to a semiconductor integrated circuit (driver IC) that drives a display, such as an LCD for instance, using the color display method of the present invention.
2. Description of the Related Art
A conventional color LCD driver IC receives input image data units from a microprocessing unit, i.e. MPU, or other type of data processing unit. Conventional image data units consists of eight data bits per pixel specifying a red, green and blue (RGB) color tone combination for each pixel. The eight data bits of each pixel's image data unit are composed of three bits for specifying a red color (R) tone, three bits for specifying a green color (G) tone, and two bits for a for specifying a blue color (B) tone. The image data is successively written to a RAM built within the driver IC. Since 23 is 8 and 22 is 4, the eight data bits of a conventional image data unit can specify 8×8×4, or 256, colors tone combinations for display. This feature is shown in FIG. 5.
In FIG. 5, three bits, D7-D5, of one pixel's image data unit, bits D7-D0, that are input from the MPU can represent up to eight different color tones, or color gradients, for the color red. Similarly, the next three bits, D4-D2, can represent up to eight color tones for the color green, and the last two bits, D1-D0, can represent up to four color tones for the color blue.
Additionally, Japanese laid-open patent application 6-167959 describes a color display control apparatus that realizes a display for simultaneous coloring of 256 colors. The display control apparatus provides a latch circuit for four data input lines of a random access memory digital to analog converter, RAMDAC, that is not conventionally used to latch display data, and combines the same with display data that is input to four data input lines of a RAMDAC that is conventionally used.
In any case, the range of color tones that can be displayed is determined by the number of bits in each pixel's image data unit that are input to a driver IC (a color display control apparatus) from an MPU. Since the number of bits per image data unit that is commonly available to color LCD driver ICs is eight bits, the range of color tones that can be displayed are commonly limited to a continuous range of 0-255, or 256, colors tones.
However, in recent years, additional diversification of color tones in color displays has been sought, and there are cases where the available continuous range of 256 color tones cannot meet the demands of users.